The present invention relates to improvements in apparatus and methods for forming reclosable plastic bags, and more particularly to an improved method and mechanism for forming edge seams on adjacent bags which are cut to separate the bags.
In the manufacture of plastic bags, one form of manufacture employs material that is sealed by the application of heat and pressure opposed overlaid sheets of plastic from the front and back walls of a bag with a reclosable interlocking rib and groove plastic zipper along the top. Such sheets are continuous and separate bags are formed by sealing jaws which apply heat and pressure at the edges of the bag and cut the continuous length of film to separate adjacent bags.
In one well known form of the manufacture which is frequently referred to as a form, fill and seal process, thermoplastic material is fed forwardly and wrapped over a filling tube. At the edges of the plastic material, is an interlocking zipper. The material is fed downwardly over the filling tube and contents are dropped through the tube to fill individual bags. Individual bags are cut from the continuous length by heated sealing jaws being pressed at bag intervals and the resultant seam is cut intermediate its sides to separate individual bags which have seams running along their sides. As a seam is formed and the finished bag is cut, the contents are dropped into the bag and it is pulled downwardly whereupon a new seam is formed above the contents. Examples of this type of bag manufacture are illustrated in U.S. Pat. Nos. 4,709,533, Ausnit, and 4,617,683, Christoff and Ausnit. This arrangement of bag manufacture employs relatively high speed operation with the tubular material being incrementally pulled down over the filling tube and cut and cross-sealed. The integrity of the seam formed by the cross-seal depends upon the amount of heat transmitted to the plastic. It is essential that a complete integral seal be formed by supplying sufficient heat to the plastic to cause the overlaid sheets to melt at the seam edge but the heat must not be at a level so that melt holes are formed adjacent the seam in the bag plastic. Yet, the heat which is transmitted to the plastic must be sufficient to cause complete sealing. Difficulties are encountered in high speed operation varying from incomplete joining of the layers to form the seam to openings inadvertently caused in the plastic by the heated sealing jaws.
It is accordingly an object of the present invention to provide an improved method and apparatus for cross-seaming plastic bags such as in a form, fill and seal operation wherein the seams are of improved integrity and strength.
A further object of the present invention is to provide an improved cross-seaming apparatus and method for the formation of edge seams for bags wherein an improved appearing seam is formed and one which eliminates perforations and insures a more secure seam.
A further object of the invention is to provide an improved seaming apparatus and method wherein variances can be accommodated in the speed of seaming and operation without adversely affecting the integrity of the seams which are formed.
Another further object of the invention is to provide a cross-seaming apparatus and method for forming side seams in bags wherein a thicker amount of plastic occurs at the top of the bag due to the presence of an interlocking rib and groove fastener and wherein the seaming apparatus and method accommodates this thicker plastic without adversely affecting the integrity of the seam.